1. Field of the Invention
The present invention relates to a traffic engineering apparatus which performs traffic engineering, a network system equipped with the traffic engineering apparatus, a traffic control method and traffic control program which control traffic flow rates.
2. Description of the Related Art
With the spread of the Internet, the number of domains connected to the Internet is growing steadily. The internet is a collection of networks known as domains. The domain is a network managed by a single management body with consistent policy. Communications are established among domains by exchanging their route information using an interdomain routing protocol.
Currently, BGP4 is used as an interdomain routing protocol on the Internet (see Y. Rekhter, T. Li, and S. Hares, “A Border Gateway Protocol 4 (BGP-4),” RFC 4271, Internet Engineering Task Force, 2006). In BGP4 terminology, a domain is referred to as an AS (Autonomous System).
When communicating using BGP4, an AS informs an adjacent AS of an address prefix in the local AS. Then, the informed AS (specifically, a BGP router) informs next adjacent AS of the address prefix by attaching its own AS number. In this way, when an address prefix is announced from an AS, the address prefix propagates from AS to AS with an AS number being attached by each AS which passes the address prefix.
FIG. 19 is an explanatory diagram showing how an address prefix propagates using BGP. AS 1 attaches its own AS number “1” to an address prefix “192.168.1.0/24” in the local AS. Then, AS 1 transmits a BGP UPDATE message to adjacent ASes, namely, AS 2 and AS 3 with its own AS number attached. Upon receiving the BGP UPDATE message, AS 2 and AS 3 transmit BGP UPDATE messages to their adjacent ASes with their respective AS numbers attached. Similarly, upon receiving the BGP UPDATE message, each AS transfers a packet whose address matches the address prefix to the AS from which the BGP UPDATE message has been received.
In the example shown in FIG. 19, AS 5 receives BGP UPDATE messages whose address prefix is “192.168.1.0/24” from adjacent AS 2 and AS 4. AS 5 compares an AS PATH attribute attached to the address prefix in the BGP UPDATE messages received respectively from AS 2 and AS 4. Then, AS 5 adapts the BGP UPDATE message which has the shorter AS PATH length. In the example shown in FIG. 19, a BGP UPDATE message 1913 has an AS PATH length of 2 while a BGP UPDATE message 1915 has an AS PATH length of 3. Consequently, AS 5 adapts the BGP UPDATE message 1913 and transfers the packet.
A routing protocol by which an address prefix is propagated with the AS numbers of ASes on the route being recorded as described above is known as a path vector routing protocol.
Next, traffic engineering using BGP will be described with reference to FIG. 20. AS 1 divides the address prefix “192.168.1.0/24” in the local AS into two address blocks “192.168.1.0/25” and “192.168.1.128/25”. Then, AS 1 transmits the respective address blocks to different ASes using BGP UPDATE messages. Consequently, packets addressed, for example, to “192.168.1.1” out of addresses in the AS 1 arrive at AS 1 only via a link connected to AS 2. On the other hand, packets addressed, for example, to “192.168.1.129” arrive at AS 1 via a link connected to AS 3.
However, an apparatus which performs traffic engineering (hereinafter also referred to as TE) using BGP cannot control a propagation range of BGP UPDATE messages. This extends the propagation range of BGP UPDATE messages. Consequently, when ASes perform TE one after another, the number of BGP UPDATE messages increases, resulting in an increased processing load of the BGP UPDATE messages.
In the implementation example of TE shown in FIG. 20, AS 1 divides the address prefix in the local AS into two address blocks and informs other ASes of the two address blocks using different BGP UPDATE messages. However, it can be seen that the number of messages has been increased in the example of FIG. 20 compared to the example of FIG. 19 in which TE is not performed.